It's melanin Monday (not a real thing — but it should be), time to brush up on your knowledge of all things pigment-related! People with fair skin and rosy locks get their distinctive looks from mutations in the gene that codes for melanocortin 1 receptor, a protein that aids in the synthesis of the pigment melanin; but there is also a growing body of evidence that suggests folks with the redhead phenotype actually experience pain differently than the rest of us. Everyone, it's time you learned about the painful secrets of the crimson coif.
For years, there existed a well-established anecdotal impression within the medical community that redheads require more anesthetic than the typical patient. This could have meant any number of things, including:
1) Redheads just like to complain about going under the knife.
2) There is a widespread, sadistic (and perhaps subconscious) prejudice against redheads within the anesthesiologist community.
3) Redheads actually have different sensitivity to pain compared to people with other hair colors.
In 2004 and 2005, two studies led by anesthesiologist Edwin B. Liem and funded by the National Institutes of Health helped explore these options in greater detail, and found compelling evidence for choice number 3.
The first study revealed that redheads are more sensitive to thermal pain (i.e. perception of pain brought on by excessive cold and heat), and that they're also more resistant to the pain-numbing effects of certain anesthetics. The second study found that redheads required, on average, 19% more anesthetic than dark-haired (black or brown-haired) women. (Interestingly, neither study recruited blonde test participants.)
But the life of a redhead isn't all pain and suffering; a study led last year by researcher Lars Arendt-Nielson revealed that redheaded women are actually less sensitive to stinging sensations (like that of a pinprick) than either blondes or brunettes. So what's going on here? Researchers aren't entirely sure, but one hypothesis ties back — perhaps unsurprisingly — to redheads' mutant melanocortin 1 receptor (MC1R).
Like most cell surface receptors, MC1R's activity is regulated by the binding of a specific set of complementary proteins. When it comes to pigment production, those proteins are called melanocyte stimulating hormones (MSH). In 98% of the population, MSH cause MC1R to production dark eumelanin, but in redheads, their mutant MC1R lead to the production of a red-tinged pheomelanin, instead. But here's the catch: melanocortin 1 receptors also interact with molecules that are structurally similar to melanocyte stimulating hormones, including hormones called endorphins. Endorphins have a whole bunch of physiological functions, but one of their primary roles is one of pain relief. Just remember: "endorphin" stands for "endogenous morphine," and morphine is a powerful painkiller.
If mutations in MC1R can lead to changes in melanin production, it stands to reason that the same mutations could have an effect on the body's ability to take signals from analgesic endorphins. By improving our understanding of the interaction between endorphins and MC1R, we can get a better handle on the strange way redheads experience pain.